ALSA: usb-audio: Fix NULL pointer deref in snd_usb_power_domain_set()

ALSA: usb-audio: Fix NULL pointer deref in snd_usb_power_domain_set()

Commit adding support for multiple control interfaces expanded struct
snd_usb_power_domain with pointer to control interface for proper control
message routing but missed one initialization point of this structure,
which has left new field with NULL value.

Standard mandates that each device has at least one control interface and
code responsible for power domain does not check for NULL values when
querying for control interface. This caused some USB devices to crash
the kernel.

Fixes: 6aa8700150f7 ("ALSA: usb-audio: Support multiple control interfaces")
Signed-off-by: Karol Kosik <k.kosik@outlook.com>
Link: https://patch.msgid.link/AS8P190MB1285B563C6B5394DB274813FEC782@AS8P190MB1285.EURP190.PROD.OUTLOOK.COM
Signed-off-by: Takashi Iwai <tiwai@suse.de>